Direct positive photographic emulsion stabilized against development stain

ABSTRACT

A DIRECT POSITIVE PHOTOGRAPHIC EMULSION AND LIGHT SENSITIVE ELEMENT HAVING A PRE-FOGGING AGENT, A SILVER HALIDE, AND CONTAINING A MEROCYANINE DYE REPRESENTED BY THE GENERAL FORMULA:   2-(R1-N(-R3)-),4-(O=),5-((-N(-R)-Z-)&gt;C=(L1-L2)N=)-   2-THIAZOLINE   WHEREIN Z REPRESENTS A GROUP WHICH COMPLETES A THIAZOLINE NUCLEUS, AN OXAZOLINE NUCLEUS, OR PYRROLINE NUCLEUS; R REPRESENTS AN ALKYL GROUP OR A SUBSTITUTED ALKYL GROUP, L1 AND L2 EACH REPRESENTS A METHINE GROUP OR A SUBSTITUTED METHINE GROUP; R1 AND R2 EACH REPRESENTS AN ARYL GROUP; AND N REPRESENTS O, 1 OR 2.

nited States Patent O 3,627 534 DIRECT POSITIVE PHOTOGRAPHIC EMULSION STABILIZED AGAINST DEVELOPMENT STAIN Keisuke Shiba, Masanao Hinata, Akira Sato, and Motohiko Tsubota, Kanagawa, Japan, assiguors to Fuji Photo Film (30., Ltd., Kanagawa, Japan No Drawing. Filed Feb. 20, 1969, Ser. No. 801,180 Claims priority, application Japan, Feb. 21, 1968, 43/ 10,877 Int. Cl. G03c 1/10 US. Cl. 96-135 13 Claims ABSTRACT OF THE DISCLOSURE A direct positive photographic emulsion and light sensitive element having a pre-fogging agent, a silver halide, and containing a merocyanine dye represented by the general formula:

wherein Z represents a group which completes a thiazoline nucleus, an oxazoline nucleus, or pyrroline nucleus; R represents an alkyl group or a substituted alkyl group, L and L each represents a methine group or a substituted methine group; R and R each represents an aryl group; and n represents 0, l or 2.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates generally to silver halide photographic emulsions and more particularly to direct positive photographic emulsions.

In general, the photographic density of a silver image obtained by light exposure and development of a photographic light-sensitive element becomes higher as the amount of the light exposure increases, but occassionally, when the amount of the light exposure reaches a given value, the photographic density reaches a maximum value and when the image is further exposed, a reversal phenomenon occurs and the photographic density degrades to below the maximum value. This reversal phenomenon is called solarization. In other words, when an area where the solarization will occur is exposed over the maximum exposure value, the photographic density is reduced and hence a positive image is obtained there. The present invention is concerned with a direct positive photographic emulsion wherein this phenomenon is utilized.

(2) Description of the prior art It is well known that a direct positive image can be obtained when a direct positive photographic lightsensitive element using a solarization-type photographic emulsion is exposed and developed. The solarization emulsion is a silver halide photographic emulsion which has been previously fogged in an amount corresponding to the aforesaid maximum photographic density.

Such direct positive photographic elements are used for documents copying, etc., and the images obtained tend to have a considerable contrast, that is, they tend to become hard, Therefore, a direct positive photographic element capable of providing a photographic miage of as soft as possible is desired, and it becomes necessary to reduce the contrast of image while maintaining a definite maximum density (D max.). For this purpose, a method was proposed in the specification of British Pat. No. 1,054,284 wherein the contrast of a photographic image was reduced by incorporating a merocyanine dye in a solarization-type photographic emulsion. The reduction of contrast depends upon thekind of the sensitizing dye, and the concentration of the dye in the emulsion. When a given sensitizing dye is considered, the rate of reduction in contrast increases as the concentration of the dye in the emulsion increases.

On the other hand, such methods are usually accompanied with a deficiency in that the sensitizing dye remains in emulsion layer after photographic processing in order to provide stains and the stain formation becomes more severe as the concentration of dye in the emulsion increases.

Accordingly, in a solarization-type photographic lightsensitive element having an emulsion layer containing a sensitizing dye (which causes the reduction in contrast, but at the same time causes the formation of stains after development), a light white background cannot be obtained when black and white photography is used. Also, the reproduction of true colors becomes impossible when color photography is attempted.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a direct positive photographic emulsion which is preliminarily fogged and has a high maximum density (D max.) and low contrast,

Another object of this invention is to provide previously fogged direct positive photographic emulsion wherein the formation of stains after development, due to the presence of a sensitizing dye is reduced and thus reduces contrast.

DESCRIPTION OF THE INVENTION The objects of the present invention can be achieved by incorporating in a previously fogged direct positive photographic emulsion a sensitizing dye represented by the following general Formula I:

wherein Z represents a group which forms a thiazoline nucleus, an oxazoline nucleus, or a pyrroline nucleus; R represents an alkyl group of a substituted alkyl group; L and L each represents a methine group or a substituted methine group; R and R each represents an aryl group; and n is 0, 1 or 2.

That is, Z, in the above formula, is a group that forms a thiazoline nucleus, such as thiazoline, 4-methyl thiazoline; and oxazoline nucleus, such as oxazoline, 4 methyloxazoline, 4,4-dimethyloxazoline, etc.; or pyrroline nucleus, such as pyrroline, 3-methylpyrroline, 4-methylpyrroline, 4-phenylpyrroline, S-methylpyrroline, etc. R represents an alkyl group such as methyl, ethyl, n-propyl, n-butyl, etc., or a substituted alkyl group such as fi-ethoxymethyl, fl-methoxyethyl, allyl (or vinylmethyl), benzyl, ,B-phenylethyl, carboxymethyl, fl-carboxyethyl, fl-sulfoethyl, 'y-sulfopropyl or 6-sulfobutyl. L and L represent a methine group or a substituted methine group shown by =CH or =CR'-- (wherein R represents an alkyl group or an aryl group) respectively.

The particularly effective sensitizing dye is the merocyanine dye having general Formula I wherein the heterocyclic ring is a mono-cyclic thiazoline nucelus, oxazoline nucleus, or pyrroline nucleus.

The examples of the typical merocyanine dyes represented by aforesaid general Formula I are shown below;

,' CS Rs wherein Z and -R have the same meanings as in general Formula I; R represents an alkyl group or an aryl group; and X represents an anion and a ketomethylene compound represented by the general formula:

(III) wherein R and R have the same meaning as in general Formula I in the presence of an organic base such as triethylamine.

Also, when n is 1 or 2, the merocyanine dye may be prepared by condensing an aniline derivative or an acetanilide derivative represented by the general formula:

wherein Z, R, L and L have the same meanings as in general Formula I and R represents a hydrogen atom or an acetyl group. The compound represented by general Formula III is condensed in the presence of an organic base such as triethylamine.

Example I.-Typical examples of preparing the abovementioned dyes are as follows:

Four grams of Z-(B-acetoanilidovinyl)-3-ethyl thiozolinium iodide and 2.7 g. of Z-biphenylamino thiazole-4-one were heated under reflux for 20 minutes on a water bath and in the presence of 1.5 ml. of triethylamine to cause the reaction thereof. After cooling, the dye reaction product precipitated and was purified by filtration and recrystallized from an ethanol-methanol mixed solvent to produce 1.6 g. of dye 1 above having a melting point of 275 C. The spectral absorption maximum of the dye was 458 m (in methanol).

By similar procedures dyes 3 and 4 above were prepared. The melting point and the spectral absorption maximum of dye 3 were 254 C. and 437 my. (in methanol) and those of dye 4 were 226 C. and 452 III/1.. (in methanol), respectively.

The merocyanine dye represented by aforesaid general Formula I is highly soluble in organic solvents such as methanol and ethanol, and, hence, is usually added to a silver halide emulsion in a solution of such solvents. A particularly effective amount of the dye is 30 mg. to 250 mg. per kilogram of emulsion, but the optimum concentration of dye in the emulsion depends on the type of dye and the emulsion used, and is determined by means of wellknown sensitometry.

As the silver halide emulsions used in the present invention, there may be employed various kinds of silver halides, such as silver chloride, silver bromide, silver chlorobromide, silver iodobromide, silver chloroiodobromide, and the like.

The silver halide emulsion of this invention has been previously fogged to the maximum density by light exposure or by means of a chemical fogging agent.

As chemical fogging agents that can be used to fog the silver halide in the emulsion without harmful side effects to the silver halide emulsion are, for example, thiourea, dioxide, stannous chloride, formaldehyde, and hydrazine.

After the fogging procedure is finished, usual additives such as coating aids or hardening agents may be added to the emulsion if desired. After adjusting the pH and the silver ion concentration of the silver halide emulsion, if necessary, a solution of the merocyanine dye is added to the emulsion with stirring and the resulting emulsion is applied to a support.

As the support, there may be employed, e.g., a glass plate, a cellulose derivative film such as triacetyl cellulose film, a synthetic resin film such as polyethylene terephthalate film, or a baryta-coated paper.

The previously fogged silver halide emulsion of this invention contains the merocyanine dye represented by general Formula I, mentioned above, and the dye causes a reduction in contrast. Hence, the emulsion can be effectively used for soft direct positive photographic light-sensitive elements, such as copying light-sentitive elements for X- ray photographs. Also, the direct positive photographic light-sensitive elements having a layer of the silver halide emulsion of the present invention gives a film image with less color. That is, a film having significantly fewer stains, a reduction in contrast can be attained without lowering the maximum density (D max.).

The invention can be seen more practically by the following illustrative example.

Example II.A silver bromide emulsion fogged to the maximum density by means of hydrazine dihydrochloride was prepared, and the pH and pAg of the emulsion were adjusted to 6.0 and 9.0, respectively. The emulsion was divided into proportions, and each of the merocyanine dyes shown below was added to one of the emulsions and thereafter the emulsions were applied to triacetyl cellulose films and then dried.

The light-sensitive film, thus prepared, was exposed through an optical step wedge and developed in an aqueous developer having the following composition;

G./l. p-Methylaminophenol sulfate 4 Hydroquinone Sodium sulfite (anhydrous) 60 Sodium carbonate (anhydrous) 2.5

The developed emulsion layer was then fixed in a conventional fixing solution containing sodium thiosulfate and, after washing, was dried. The optical density of the positive image, thus obtained, was measured by means of a sensitometer and the gamma value was determined. The results are shown in Table 1.

TABLE 1 S tail-l Dye No. Gamma D max. density *A conventional (lye having the formula:

The density of stains shown in Table 1 was measured as follows. After exposing the sample to give the minimum density (D min.), the sample was developed in the aforesaid developer for one minute, fixed for 10 minutes, washed, and dried. The stain density of the thus processed sample was detained using a green filter having a transmission maximum at 525 m. The stain density of the sample wherein no dye was added was shown as 0.

What is claimed is:

1. A preliminarily fogged direct positive silver halide photographic emulsion containing at least one merocyanine dye represented by the general formula:

wherein Z represents a group which completes a member selected from the group consisting of a thiazoline nucleus, an oxazoline nucleus, and a pyrroline nucleus; R represents a member selected from the group consisting of a lower alkyl group and a substituted lower alkyl group whose substitutents are members selected from the group consisting of lower alkoxy lower alkyl, allyl, aryl lower alkyl, carboxy lower alkyl, and sulfo lower alkyl; L and L each represents a member selected from the group consisting of a methine group and a substituted methine group, said substituent being a member selected from the group consisting of a lower alkyl group and an aryl group; and n represents 0, 1, or 2.

2. The photographic emulsion of claim 1 wherein the amount of said merocyanine dye is 30-250 mg. per kilogram of emulsion.

3. The photographic emulsion of claim 1 wherein said silver halide emulsion has been fogged by light exposure.

4. The photographic emulsion of claim 1 wherein said silver halide has been fogged by a chemical fogging agent.

5. The photographic emulsion of claim 4 wherein said chemical fogging agent is thiourea, dioxide, stannous chloride, formaldehyde, or hydrazine.

6. A silver halide photographic light-sensitive element having a layer of a preliminarily fogged direct positive silver halide photographic emulsion containing at least one merocyanine dye represented by the general formula:

wherein Z represents a group which completes a member selected from the group consisting of a thiazoline nucleus,

an oxazoline nucleus, and a pyrroline nucleus; R represents a member selected from the group consisting of a lower alkyl group and a substituted lower alkyl group whose substituents are members selected from the group consisting of lower alkoxy lower alkyl, allyl, aryl, aryl lower alkyl, carboxy lower alkyl, and sulfo lower alkyl; L and L each represents a member seected from the group consisting of a methine group and a substituted methine group, said substituent being a member selected from the group consisting of a lower alkyl group and an aryl group; and n represents 0, 1, or 2 on a support.

7. The photographic emulsion of claim 1, wherein the thiazoline nucleus is a member selected from the group consisting of thiazoline and 4-methyl thiazoline.

8. The photographic emulsion of claim 1 wherein the oxazoline nucleus is a member selected from the group consisting of oxazoline, 4-methyl oxazoline and 4,4-dimethyloxazoline.

9. The photographic emulsion of claim 1, wherein the pyrroline nucleus is a member selected from the group consisting of pyrroline, 3-methyl pyrroline, 4-methyl pyrroline, 4-phenyl pyrroline, and S-methyl pyrroline.

10. The photographic light-sensitive element of claim 6, wherein the amount of said merocyanine dye is 30-250 mg. per kilogram of emulsion.

11. The photographic light-sensitive element of claim 6, wherein the thiazoline nucleus is a member selected from the group consisting of thiazoline and 4-methyl thiazoline.

12. The photographic light-sensitive element of claim 6, wherein the oxazoline nucleus is a member selected from the group consisting of oxazoline and 4-methyl oxazoline.

13. The photographic light-sensitive element of claim 6, wherein the pyrroline nucleus is a member selected from the group consisting of pyrroline, 3-rnethyl pyrroline, 4-methyl pyrroline, and S-methyl pyrroline.

References Cited UNITED STATES PATENTS 3,364,026 1/1968 Rees NORMAN G. TORCHIN, Primary Examiner R. E. FICHTER, Assistant Examiner US. Cl. X.R. 96-l39, 140 

